1. Related Application
The present application claims priority to Japanese Patent Application Number 2009-277629, filed Dec. 7, 2009, the entirety of which is hereby incorporated by reference.
2. Field of the Invention
The present invention relates to a speaker apparatus that outputs sound through the vibration of a diaphragm coupled to a voice coil due to interaction between a magnetic field generated in a magnetic circuit and a sound signal electric current flowing through the voice coil.
3. Description of the Related Art
In the past, there have been proposed so-called counter drive type speaker apparatuses in which a magnetic circuit is disposed substantially in the center of a space surrounded by a cone shaped diaphragm (see Japanese Patent Application Publication No. 1987(S62)-136196, for example). In such a speaker apparatus, in addition to a frame (a basket shaped rear portion made of plastic) for housing components such as a diaphragm and a damper, another frame (a basket shaped front portion made of plastic) is disposed on the front part of the diaphragm, and the magnetic circuit is supported and secured by this front frame. A voice coil unit disposed inside a magnetic gap in the magnetic circuit is coupled to the inner circumferential edge of the diaphragm. In such a speaker apparatus, because the magnetic circuit is disposed inside the space surrounded by the cone shaped diaphragm, the space is efficiently used and thickness reduction can be achieved.
However, such a conventional speaker apparatus has a disadvantage of increased weight because, in addition to the frame for mounting and housing the diaphragm, the damper, and the like, another frame needs to be disposed on the front part of the diaphragm to mount the magnetic circuit.
Furthermore, because the diaphragm is coupled to a portion, projecting outward from the magnetic gap, of the voice coil unit disposed inside the magnetic gap formed in the magnetic circuit, the depth of the cone shaped space surrounded by the diaphragm must be set relatively large in order to ensure a space for the voice coil unit projecting outward from the magnetic gap. In addition, the length of the portion of the voice coil unit projecting outward from the magnetic gap, to which the diaphragm is coupled, cannot be made as small as it is desired because the amount of vibration of the diaphragm (the maximum vibration amount) must be taken into consideration for design. Therefore, thickness reduction is limited because the depth of the cone shaped space surrounded by the diaphragm needs to be made large to some extent and the amount of vibration of the diaphragm must be taken into consideration for designing the length of the portion, projecting outward from the magnetic gap, of the voice coil unit, for example.
Accordingly, the present invention has been devised in view of the foregoing circumstances and provides a lightweight and low-profile speaker apparatus.